1. Field of the Invention
This application relates generally to gyroscopes, and more specifically, to gyroscopes utilizing optical sensing.
2. Description of the Related Art
Known optical fiber gyroscopes (e.g., fiber-optic gyroscopes or fiber ring gyroscopes) do not have mechanical parts and are based on the Sagnac effect. While miniature mechanical gyroscopes are known (See, e.g., J. J. Bernstein, U.S. Pat. No. 5,203,208 and T. K. Tang et al., U.S. Pat. No. 5,894,090), conventional miniature mechanical gyroscopes are generally based on microelectromechanical system (MEMS) technology, and the rotation applied to the gyroscope is sensed using electrostatics or some form of magnetic sensing. The rotation sensitivity of conventional MEMS-based gyroscopes is limited, and several orders of magnitude worse than Sagnac-based optical gyroscopes.
For example, the performance of conventional MEMS-based gyroscopes is usually limited by the electronic noise, which is fairly high. Therefore, these existing gyroscopes must be operated at a mechanical resonance frequency of the structure (e.g., of the two or more oscillating plates) in order to enhance the signal resulting from the applied rotation. In order for the two plates of such conventional devices to be operated on resonance, they must exhibit at least one set of identical resonance frequencies. Achieving identical resonance frequencies requires very accurate tuning of the structural parameters during fabrication, which is often limited by fabrication tolerances. To achieve good sensitivity with such configurations, the mechanical quality factor is designed to be very large, making it very hard to design a structure in which the mechanical drive and sense frequencies match. A high quality factor also reduces the measurement bandwidth, i.e., the dynamic range of the sensor, since the bandwidth scales with the inverse of the quality factor.
As a result of these complexities, and of the fairly high electronic noise, current MEMS gyroscopes exhibit a relatively low sensitivity. A typical good MEMS gyroscope usually can detect in the range of 0.1 to 1 deg/s. See, e.g., C. Acar and A. Shkel, MEMS vibratory gyroscopes: structural approaches to improve robustness, Springer (2008). A minimum detectable rotation rate of 0.05 deg/s has also been reported. See H. Xie and G. K. Fedder, “Integrated microelectromechanical gyroscopes,” J. Aerospace Eng. Vol. 16, p. 65 (2003). There are a few reports of MEMS gyroscopes with much better sensitivities (˜10 deg/h) (see, e.g., Acar and Shkel), but they operate in vacuum and have very tightly matched drive and sense modes. See, e.g., T. K. Tang, R. C. Gutierrez, J. Z. Wilcox, C. Stell, V. Vorperian, M. Dickerson, B. Goldstein, J. L. Savino, W. J. Li, R. J. Calvet, I. Charkaborty, R. K., Bartman, and W. J. Kaiser, “Silicon bulk micromachined vibratory gyroscope for microspacecraft, “Proc. SPIE Vol. 2810, p. 101 (1996). Such configurations may be difficult to reproduce on a large scale and at a low cost.